Before water intake (at baseline), we will make the assumption that the subject is in homeostasis with adequate strength of the plasma osmolarity-decreasing effect of water reabsorption (through the water channels) as well as normal plasma and urine osmolarities (isotonic) and urine volume.

Step 1: With water intake, water leaves the plasma and osmolarity increases (concentrated, hypertonic).

Step 2: This is in the same direction as the plasma osmolarity-decreasing effect of the water reabsorption. Thus, although the strength of the plasma osmolarity-decreasing effect of water reabsorption (through the water channels) was adequate before water intake (at baseline), this strength is now too strong (red) to reverse the decreased plasma osmolarity (diluted, hyportonic) produced by water intake. Control by negative feedback is needed.

Step 3: With the strength of the plasma osmolarity-decreasing effect (through the water channels) of the water reabsorption before water intake (at baseline) being too strong (red), the negative feedback decreases (blue) the water reabsorption from the tubule.This decreases the water reabsorption from the tubule.

Step 4: With the decrease in water reabsorption, concentrated (hypertonic) solution enters the plasma. This will lead to a reverse in the decreased plasma osmolarity (diluted, hypotonic) produced by water intake, increasing it towards normal (baseline, isotonic) osmolarity. Because concentrated (hypertonic) solution leaves the tubule due to reabsorption from the tubule, the fluid remaining in the tubule has decreased osmolarity (diluted, hypotonic). Also, with the decrease in water reabsorption, there is more water remaining in the tubule. Overall, the urine becomes dulited and increases in volume.